In order to isolate the line and load stabs within a circuit breaker compartment, shield devices are proposed for installation intermediate the compartment stabs and the corresponding line and load plugs on the circuit breaker when the circuit breaker is removed from the compartment. The following U.S. patent applications disclose various shield arrangements for installation within circuit breaker compartments. "Safety Shield Assembly For a Drawout Type Circuit Breaker", Ser. No. 322,347, filed Nov. 18, 1981; "Interchangeable Shield Arrangement For a Circuit Breaker", Ser. No. 322,348, filed Nov. 18, 1981; "Shield Assembly For AKR Circuit Breaker Compartments", Ser. No. 328,336, filed Dec. 7, 1981 and "Shield Assembly For 800 to 1600 Ampere Circuit Breaker Compartments", Ser. No. 328,337, filed Dec. 7, 1981, U.S. Pat. Nos. 3,614,350, 4,183,073, and 4,285,026 also describe various mechanisms for isolating line and load stabs within circuit breaker compartments. The aforementioned patent applications and U.S. patents are incorporated herein for purposes of reference. The instant invention relates to an isolation shield mechanism for insertion within higher ampere circuit breaker compartments in the 2500-4000 ampere range which occupy a substantial portion of the available compartment space. The invention provides a fast operating shield mechanism which allows the upper and lower shields to rapidly move away from in front of the compartment power and load stabs before the circuit breaker is half way within the compartment.